Enabling OSPFv2 on an Interface Basis
Last Updated: November 1, 2011
This document describes how to enable Open Shortest Path First version 2 (OSPFv2) on a per-interface
basis to simplify the configuration of unnumbered interfaces. The ip ospf area command allows you to
enable OSPFv2 explicitly on an interface. The ip ospf area command is an alternative to enabling OSPFv2
through the address of the interface that matches the address range specified by the network area
command.
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Finding Feature Information, page 1
Prerequisites for Enabling OSPFv2 on an Interface Basis, page 1
Restrictions on Enabling OSPFv2 on an Interface Basis, page 2
Information About Enabling OSPFv2 on an Interface Basis, page 2
How to Enable OSPFv2 on an Interface Basis, page 3
Configuration Example for Enabling OSPFv2 on an Interface, page 4
Additional References, page 5
Feature Information for Enabling OSPFv2 on an Interface Basis, page 6
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest feature
information and caveats, see the release notes for your platform and software release. To find information
about the features documented in this module, and to see a list of the releases in which each feature is
supported, see the Feature Information Table at the end of this document.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support.
To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Prerequisites for Enabling OSPFv2 on an Interface Basis
OSPFv2 must be running on your network.
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Benefits of Enabling OSPFv2 on an Interface Basis
Restrictions on Enabling OSPFv2 on an Interface Basis
Restrictions on Enabling OSPFv2 on an Interface Basis
The ip ospf area command is supported only for OSPFv2.
Information About Enabling OSPFv2 on an Interface Basis
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Benefits of Enabling OSPFv2 on an Interface Basis, page 2
Implications of Configuring OSPFv2 On a Router Basis or an Interface Basis, page 2
Benefits of Enabling OSPFv2 on an Interface Basis
OSPF is enabled on an interface when the network address for the interface matches the range of addresses
that is specified by the network area command, which is entered in router configuration mode.
Alternatively, you can enable OSPFv2 explicitly on an interface by using the ip ospf area command, which
is entered in interface configuration mode. This capability simplifies the configuration of unnumbered
interfaces with different areas.
Because the ip ospf area command is configured explicitly for an interface, it supersedes the effects of the
network areacommand, which is entered at the network level to affect the interfaces whose addresses fall
within the address range specified for the network area command.
If you later disable the ip ospf area command, the interface still will run OSPFv2 as long as its network
address matches the range of addresses that is specified by the network areacommand.
Implications of Configuring OSPFv2 On a Router Basis or an Interface Basis
Before you use the ip ospf area command to enable OSPFv2 on an interface, we recommend that you
understand the following scenarios and command behavior. There are implications to using the network
areacommand (configuring OSPFv2 in router configuration mode) versus using the ip ospf area command
(configuring OSPFv2 in interface configuration mode).
Interface Is Already OSPFv2-Enabled by network area Command with Same Area and Process
If you enter the ip ospf area command on an interface that is enabled in OSPFv2 by the network
areacommand, the process ID or area ID of the interface does not change, and the interface status will not
be changed. However, the interface will be flagged as being configured from interface configuration mode,
and the configuration data will be saved in the interface description block (IDB).
Interface Is Already Configured by network area Command with Different Area or Process
If you enter the ip ospf area command on an interface that is enabled in OSPFv2 by the network
areacommand, but you change the configuration by changing the process ID and area ID of the interface,
after the new configuration information is stored in the IDB, the interface will be removed and reattached.
Therefore, the interface will be removed from the original area and process and be added to the new ones.
The state of the interface will also be reset.
Interface Is Not Configured by network area Command
If the interface is not enabled in OSPFv2 by the network area command, the area and OSPF router
instance will be created if needed. When the router is reloaded, the OSPF process will not begin running
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Enabling OSPFv2 on an Interface
How to Enable OSPFv2 on an Interface Basis
until system initialization is complete. To remove an OSPF router instance, enter the no router ospf
command. Removing the ip ospf area command in interface mode will not result in removing an OSPF
router instance.
Removing an ip ospf area Command
When the ip ospf areacommand is removed, the interface will be detached from the area. The area will be
removed if it has no other attached interfaces. If the interface address is covered by the network area
command, the interface will be enabled once again in the area for the network that it is in.
New Processes
If an OSPF process does not already exist, and a router ID cannot be chosen when either the router ospf
command or the interface command is configured, a Proximity Database (PDB) and a process will be
created, but the process will be inactive. The process will become active when a router ID is chosen, either
when it is explicitly configured using the router-id command or when an IP address becomes available.
Note that the router ospf command will now be accepted even if a router ID cannot be chosen, putting the
command-line interface (CLI) into the OSPF configuration context. Therefore, the router-id command is
to be entered before an IP address is available. If the process is not active and the show ip ospfcommand is
entered, the message "%OSPF: Router process X is not running, please provide a router-id" will be
displayed.
Link-State Advertisements and Shortest Path First
If a state change occurs as a result of the ip ospf areacommand, new router link-state advertisements
(LSAs) will be generated (also for the old area, if the interface is changing areas) and shortest path first
(SPF) will be scheduled to run in both the old and new areas.
How to Enable OSPFv2 on an Interface Basis
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Enabling OSPFv2 on an Interface, page 3
Enabling OSPFv2 on an Interface
SUMMARY STEPS
1. enable
2. configure terminal
3. interface type number
4. ip ospf process-id area area-id [secondaries none]
5. end
6. show ip ospf interface [type -number]
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Enabling OSPFv2 on an Interface
Configuration Example for Enabling OSPFv2 on an Interface
DETAILED STEPS
Command or Action
Purpose
Step 1 enable
Enables privileged EXEC mode.
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Enter your password if prompted.
Example:
Router> enable
Step 2 configure terminal
Enters global configuration mode.
Example:
Router# configure terminal
Step 3 interface type number
Configures an interface type and enters interface configuration
mode.
Example:
Router(config)# interface FastEthernet 0/2/1
Step 4 ip ospf process-id area area-id [secondaries none]
Enables OSPFv2 on an interface.
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Example:
To prevent secondary IP addresses on the interface from
being advertised, you must enter the optional secondaries
keyword followed by the none keyword.
Router(config-if)# ip ospf 1 area 0
secondaries none
Step 5 end
Exits interface configuration mode and returns to privileged
EXEC mode.
Example:
Router(config-if)# end
Step 6 show ip ospf interface [type -number]
Displays OSPF-related interface information.
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Example:
Once you have enabled OSPFv2 on the interface, you can
enter the show ip ospf interfacecommand to verify the
configuration.
Router# show ip ospf interface FastEthernet
0/2/1
Configuration Example for Enabling OSPFv2 on an Interface
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Example Enabling OSPFv2 on an Interface, page 5
Example Enabling OSPFv2 on an Interface
Additional References
Example Enabling OSPFv2 on an Interface
In the following example, OSPFv2 is configured explicitly on GigabitEthernet interface 0/0/0:
Router(config)# interface GigabitEthernet 0/0/0
Router(config-if)# bandwidth 10000
Router(config-if)# ip address 172.16.1.1 255.255.255.0
Router(config-if)# ip ospf hello-interval 1
Router(config-if)# ip ospf 1 area 0
When the show ip ospf interface command is entered, the following output shows that GigabitEthernet
interface 0/0/0 was configured in interface configuration mode to run OSPFv2. The secondary IP addresses
on the interface will also be advertised:
Router# show ip ospf interface GigabitEthernet 0/0/0
GigabitEthernet0/0/0 is up, line protocol is up
Internet Address 172.16.1.1/24, Area 0
Process ID 1, Router ID 172.16.11.11, Network Type BROADCAST, Cost: 10
Enabled by interface config, including secondary ip addresses
Transmit Delay is 1 sec, State DR, Priority 1
Designated Router (ID) 172.16.11.11, Interface address 172.16.1.1
Backup Designated router (ID) 172.16.22.11, Interface address 172.16.1.2
Timer intervals configured, Hello 1, Dead 4, Wait 4, Retransmit 5
oob-resync timeout 40
Hello due in 00:00:00
Supports Link-local Signaling (LLS)
Index 2/2, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 1
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 172.26.22.11 (Backup Designated Router)
Suppress hello for 0 neighbor(s)
Additional References
The following sections provide references related to enabling OSPFv2 on an interface.
Related Documents
Related Topic
Document Title
Configuring OSPF
Configuring OSPF
OSPF commands
Cisco IOS IP Routing: OSPF Command Reference
Cisco IOS master command list, all releases
Cisco IOS Master Command List, All Releases
Standards
Standard
Title
No new or modified standards are supported by this -feature, and support for existing standards has not
been modified by this feature.
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Example Enabling OSPFv2 on an Interface
Feature Information for Enabling OSPFv2 on an Interface Basis
MIBs
MIB
MIBs Link
No new or modified MIBs are supported by this
feature, and support for existing MIBs has not been
modified by this feature.
To locate and download MIBs for selected
platforms, Cisco IOS XE releases, and feature sets,
use Cisco MIB Locator found at the following
URL:
http://www.cisco.com/go/mibs
RFCs
RFC
Title
RFC 2328
OSPF Version 2
Technical Assistance
Description
Link
The Cisco Support and Documentation website
provides online resources to download
documentation, software, and tools. Use these
resources to install and configure the software and
to troubleshoot and resolve technical issues with
Cisco products and technologies. Access to most
tools on the Cisco Support and Documentation
website requires a Cisco.com user ID and
password.
http://www.cisco.com/cisco/web/support/
index.html
Feature Information for Enabling OSPFv2 on an Interface
Basis
The following table provides release information about the feature or features described in this module.
This table lists only the software release that introduced support for a given feature in a given software
release train. Unless noted otherwise, subsequent releases of that software release train also support that
feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support.
To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
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Example Enabling OSPFv2 on an Interface
Table 1
Feature Information for Enabling OSPFv2 on an Interface Basis
Feature Name
Releases
Enabling OSPFv2 on an Interface Cisco IOS XE Release 2.1 Cisco
Basis
IOS XE Release 2.6
Note This feature was originally
named "Area Command in
Interface Mode for
OSPFv2."
Feature Information
This document describes how to
enable OSPFv2 on a per-interface
basis to simplify the
configuration of unnumbered
interfaces. The ip ospf area
command allows you to enable
OSPFv2 explicitly on an
interface. The ip ospf area
command is an alternative to
enabling OSPFv2 through the
address of the interface that
matches the address range
specified by the network area
command.
The following commands are
introduced or modified in the
feature documented in this
module:
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ip ospf area.
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Third-party trademarks mentioned are the property of their respective owners. The use of the word partner
does not imply a partnership relationship between Cisco and any other company. (1110R)
Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be
actual addresses and phone numbers. Any examples, command display output, network topology diagrams,
and other figures included in the document are shown for illustrative purposes only. Any use of actual IP
addresses or phone numbers in illustrative content is unintentional and coincidental.
© 2011 Cisco Systems, Inc. All rights reserved.
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